I think you’ll find that yesterday is there functioning as an attributive noun, not as an adjective. Compare yesterday’s newspaper, which is legal and normal, with the invalid *yesterday newspaper.
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tchristDec 25 '13 at 17:27

The fact that ‘last’ is an adjective does not mean ‘yesterday’ has to be. ‘This’, ‘any’, and ‘an’ are not adjectives, but you can replace ‘last’ or ‘yesterday’ with any one of them.
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Janus Bahs JacquetDec 25 '13 at 23:16

Hello, and Welcome to EL&U. We like answers to be fact based, not solely opinion based, and as such, love to see links to sources which support your answer.
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medicaDec 26 '13 at 10:10

(It doesn't mention Shakespeare’s “...And all our yesterdays have lighted fools the way to dusty death.” which shows yesterday acting a lot like a noun. I suppose they’d say that’s just Shakespeare playing with words.)

In a case like "I have an important meeting tomorrow," it seems as if they're nouns.

CGEL spends several pages on “temporal location expressions”. They are sometimes but not always adverbs. Several examples are given of noun phrases that specify time: I have an important meeting [Tuesday / tomorrow / the day after tomorrow / every day / next month / right this minute]. That is, certain noun phrases can be tacked onto a sentence in just the same way as an adverb or a prepositional phrase.

But what about "Yesterday afternoon?"

Here the pronoun yesterday functions as a determiner. This is not something pronouns normally do; it's an oddball case.

Determiners include the bolded expressions in twelve angry men, my red tennis shoes, a sandwich, your father's truck, three or four billion dollars. A singular count noun generally needs a determiner in front of it if it's going to function as, say, the subject of a sentence. Compare: [This afternoon / Yesterday afternoon / Afternoon] was great.

Apparently the days of the week can also serve as determiners this way: Sunday afternoon.

I’m not sure why you say that pronouns normally do not act as determiners—the most deictic of all pronouns, the demonstrative pronouns, also function as determiners (in some contexts being even forced into determinerhood): “That is a red car” vs. “That car is red”. Shakespeare’s usage may not be mentioned, but there is little doubt that these time terms can also function as true nouns with determiners: “I’d rather have a yesterday too much than a tomorrow too little” / “I’d rather have too many yesterdays than too few tomorrows”. It’s just that they don’t commonly function like that.
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Janus Bahs JacquetSep 26 '13 at 9:25

CGEL categorizes the demonstratives (this, that, these, those) and many other words traditionally considered pronouns (several, my, yours) as determinatives. This is a nice analysis because it lets them unify the treatment of That is a red car with other cases where determiners serve as NP heads, like Three or four were left or I saw your truck, but I didn’t see your father’s. However it does leave yesterday afternoon as an oddball case. Hmmm.
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Jason OrendorffSep 27 '13 at 19:39

I think I should edit the answer to address the point about demonstrative pronouns, but I’m not sure how to do it without misrepresenting CGEL. Any suggestions?
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Jason OrendorffSep 27 '13 at 19:40

Yesterday is Sunday (?) Grammatically, maybe, but not logically. Why did you write yesterday with a capital letter, in your second example? There are other mistakes, mainly formatting, in your posted answer which you probably missed. You can always edit and improve the quality of your answer.
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Mari-Lou ASep 26 '13 at 9:22

In I will go there yesterday, "yesterday" answers to the question "when?", therefore it's an adverb. We are talking about yesterday, the question is "what?" (About what are we talking?) - it's a noun. I am reading yesterday paper, "yesterday" becomes an adjective, as it answers the question "What kind of paper?"
From personal learning and then teaching experience.

There is no such thing as a “yesterday newspaper”.
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tchristApr 11 '13 at 10:52

1

But someone might describe a phone (like, say the Nokia 1202) with "That is so yesterday!" which is presumably an adjective. But yes, yesterday can't be used attributively as "a yesterday phone"; it would be "yesterday's phone" (extending the use of yesterday in this case)
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Andrew Leach♦Apr 11 '13 at 11:07

2

I will go there yesterday requires time travel! I will go is future; yesterday is in the past! Also, you can't say yesterday paper: it should be yesterday's paper - the paper issued yesterday. And it does NOT answer the question "What kind of paper?": it answers the question "Which paper?"
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TrevorDMay 11 '13 at 16:50

They are actually both considered adverbs in the uses from your example.

One bit of evidence for this is that you could replace tomorrow in your example sentence with other time adverbs, or a word like frequently or daily, but you couldn't replace it with something that is a noun only, like "office", or even "5 PM".